Metal pipe having a rolled thread



Feb. 16,1954 FINCH 2,669,469

METAL PIPE HAVING A ROLLED THREAD Filed Oct. 12, 1950 INVENTOR Harry 1. F/hc/r m. 94%] Patented Feb. 16, 1954 METAUPIPE HAVING A ROLLED THREAD Harry .L'Finch, Oil City, Pa., assignor to Jones& Laughlin 'Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Original application April 28, 1949., Serial No.

Divided and this application October 12, 1950,"Serial No. 189,828

2 Claims. (01. 285-I58) This invention relates to: -=meta1 pipe having a rolled thread. .It comprehends new and im proved metal pipe having a thread rolled thereinto whereby important advantages :in the SllI' llture and use of the'threaded pipe'are obtained. This application is a division of my copending application Serial No. 90,071, filed April 28, 1949.

.Metal pipe :of certain characteristics "may be threaded byrolling. Relatively thin-walled pipe or tubing and heavier-Walled pipe of sufficient ductility may be thus threaded. For purposes of explanation and illustrationl shall discuss thinwalled steel tubing .having a rolled thread although my invention. isnotlimited in all of its aspects to such tubing but may be otherwise embodied.

Lengths of thin-walled steel tubing are fastened together end to endtozmake long tubes for various purposes, as for example, so-called shot hole casing. Desirably each length or section is somewhat expanded at one end so that it will telescope with the unexpanded opposite end of a similar section and threads are rolled into the telescoping ends so that they may be screwed together. The thread rolling operation is rapid and economical and 'for relatively thin-walled pipe and pipe of sufiicient ductility is far less costly than cutting threads. by the. conventional method; moreover, a stronger and otherwise superiorproducttisproduced- It has heretofore beenproposed to roll threads into thin-walled tubular'articles but the threads which have been produced have been inferior and no practicable way of threading relatively long sections of pipe. has been developed. I. have deviseda machine for rolling threads into metal pipe which accomplishes the result in a highly accurate, efiective and efiicient manner. I have also devised a method of rolling threads into metal pipe whereby important advantages are obtained. I have also devised ainew thread form of importantly increased strength and efliciency relatively to rolled threads heretofore developed. My machine and method are claimed in my said copending-application.

:In rolling threads into thin-walled steel tubing it has heretofore been considered necessary to effect a partial shearing of themetal to sharply displace metal substantially radially to form the threads. Th .result has been a lack of uniiormity in the threads, the thread form differing' especially inv articles of steel of different characteristics,,.and being any event subject to early .failure or pulling. out under load. I have discovered that the conception that the rolled threads should be formed by a shearing, action is 'fallacious and that it 'is not necessary to so form them. On the contrary, I form a vastly superior and more uniform thread through causing a flow of the metal while avoiding any substantial shearing action. I rotate the :pipe generally about its axis and during such rro'tation simultaneously engage the pipe internally and externally at radially opposed portions thereof and squeeze the metal so as to causeit'tmfiow without any substantial shearing to form threads projecting fromonesur'face of the pipe while deforming the opposite surface so :that metal throughout the entire thickness of the snipe is flowed and reshaped during thread formation- I preferably form in the :pipe by simultaneous internal and external rolling attradiallywopposed portions thereof internal :and external :alternately arranged grooves and projections in generally helical form and during the forming of. such grooves and projections somewhat foreshorten the pipeand thereafter flowithemetaltat the grooves and projections without :any substantial shearing of the metal to form a thread at one surface of the pipe. I desirably formr in that way a thread whose side walls are substantially'parallel to eachother.

In rolling into metal pipe threads whose side walls are substantially parallel to each other it desirably rotate the pipe generally 'about' its axis and during such rotation press the metal from the surface of the pipe opposite thesurface to be threaded toward the surface to 'be "threaded, limiting "the metal flow at the crests-of the incipient threads and forcing the metal laterally generally parallel to the crests to form generally square :corners on 'the threads. 'I may form in the pipe a generally helical corrugation. "1 preferably engage the pipe internally and enternally by rotating dies which squeeze the metal of the pipe therebetween and cause rotation 0f the pipe during the threading operation and by one of the diesfiow the metal without any substantial shearing of "the metal into a thread forming cavity inth'e other die.

I roll into metal pipe threads of new and improved shapewhich are vastly stronger 'thanthe previous rolled threads both with respect to pull- .ing-out and with respect to failure under load.

substantially flat crest and throat, the opposite surface of the pipe having a helical depression whose dimension axially 'of the pipe at its buttom is not over about half the dimension of the crest of the thread axially of the pipe, the depression being disposed radially opposite the center of the thread crest, and a helical projection opposite the thread throat whose dimension axially of the pipe is at least one-third greater than the dimension axially of the pipe of the thread throat and merging by a smooth curve into the depression, the pipe at such opposite surface being entirely free from sharp corners. The side walls of the helical depression are preferably inclined toward each other and the side walls of the helical projection are preferably in-- clined toward each other and the depression and the projection preferably merge into each other. Desirably the thinnest section at the thread is at least about eighty per cent of the thickness of the pipe wall at a point removed from the thread.

By the improvements above referred to I provide greatly improved threaded pipe at high speed and low cost and of greater uniformity than pipe with rolled threads heretofore produced. Certain of my improved features may be used without others. Other details, objects and advantages of the invention will become apparent as the following description of a present preferred embodiment thereof proceeds.

In the accompanying drawings I have shown a present preferred embodiment of the invention in which Figure 1 is a cross-sectional view showing a pipe joint made of pipes threaded by use of my invention; and

Figure 2 is a greatly enlarged diagram showing in cross section at the left the shape of the dies and in cross section at the right the shape of the thread formed thereby.

The shape of the dies is of great importance in the formation of my improved threads. One of the dies is a thread forming die while the other die is a non-thread forming die which co-open ates with the thread forming die to cause the metal of the pipe to flow into the thread forming die. The dies have complementary metal forming faces, the thread forming die preferably having thereon a helical metal forming projection whose side walls are substantially parallel to each other and the non-thread forming die having thereon a helical metal forming projection whose side walls are inclined to each other, which inclined side walls extend substantially to the crest of the second mentioned projection, the projections being in axially staggered relation. The projections are shown to greatly enlarged scale in Figure 2. In that figure the thread forming die is the die 29 since it forms the threads on the inside of the box end of the pipe. The dies for operating on the pin end of the pipe are reversed, the thread forming die being the outside die. In Figure 2 the outside die 30 is a non-thread forming die. The helical metal forming projection of the thread forming die 29 is shown at T3 and the helical metal forming projection of the non-thread forming die 30! is shown at M. The side walls 15 of the projection 13 are substantially parallel to each other while the side walls Hi of the projection 14 are inclined to each other and extend substantially to the crest ll of the projection Hi. The projections 13 and M are in axially staggered relation. The inclined side walls 16 of the helical projection 74 on the die til preferably have rounded corners l8 and T9 at their top and bottom extremities respectively. The dimension of the projection l4 axially of the pipe at its crest is not over about half of the axial dimension of the projection 13. In between the convolutions of the projection '14 the face of the die 30 has a helical groove 8|] of somewhat dished shape merging through the rounded corners 19 into the inclined Walls 16 of the projection 14. Since the axial dimension of the projection H at its crest is not over about half the axial dimension of the thread forming projection 13 of the die 29 the groove 8b is of substantially greater axial dimension than the projection 13.

The end face 8| of the helical thread forming projection 13 is shown as being substantially at right angles to the side walls 15 so that the thread forming projection 13 is substantially square as shown in Figure 2. The dies co-operate so that in the threaded pipe the thinnest section at the thread is at least about eighty per cent of the thickness of the pipe wall at a point removed from the thread.

The improved results obtained by my improved dies are realized to the fullest extent through the hydraulic actuation of the dies toward each other. Hydraulic actuation plus the shape of the dies results in formation of a thread greatly superior to rolled threads heretofore produced.

As the outer die 38 moves toward the inner die 29 and engages the outer surface of the pipe it first deforms or corrugates the pipe so that in its initial stages the pipe is wavy internally and externally like corrugated iron culvert pipe. This corrugation of the pipe results in its being foreshortened, i. e., in its length being somewhat decreased. The foreshortening and corrugating process may continue for a number of revolutions, say twenty, until the inner faces of the corrugations engage the bottom of the groove between the convolutions of the thread forming projection 13. At that time the hydraulic pressure on the die allows for commencement of flow of the metal of the pipe without shearing of the metal. The non-thread forming projection M with its inclined faces and rounded corners causes the metal of the pipe to flow somewhat axially along the groove between the convolutions of the thread forming projection 13 to fill the corners of the groove and thus produce a square cornered thread. Continued hydraulic pressure consolidates and solidifies the metal so that a strong compact metallic structure results.

During the thread formation the metal is squeezed so that it is caused to flow Without any substantial shearing to form threads projecting from one surface of the pipe while the opposite surface is deformed; thus the metal throughout the entire thickness of the pipe is flowed and reshaped during thread formation. The metal flow is limited at the crests of the incipient threads and the metal is forced laterally generally parallel to the crests to form the generally square thread corners.

Figure 1 shows a joint between two sections of pipe having threads rolled thereinto in accordance with my invention. The section 82 has an internally threaded box end 83 and the section 84 has an externally threaded pin end 85. The internal threads in the box end and the external threads in the pin end are of substantially the same form except that the internal threads face inwardly and the external threads face outwardly. Since the threads are substantially square they interfit very accurately and provide the maximum resistance to pulling out. due to the form and proportions of the threaded Also,

pipe ends as above explained, the joint is exceptionally strong in tension tests to failure.

The thread proportions and dimensions are determined by the dies and are, of course, the same as the proportions and dimensions of the dies. The surface of the pipe opposite the thread has a helical depression whose dimension axially of the pipe at its bottom is not over about half the dimension of the thread axially of the pipe and the depression is disposed radially opposite the center of the thread crest. A helical projection is disposed radially opposite the thread throat. The projection and depression merge into each other through rounded corners. The helical projection opposite the thread throat has a dimension axially of the pipe at least one-third greater than the dimension axially of the pipe of the thread throat. The side walls of the helical depression opposite the thread crest are inclined toward each other and extend substantially to the bottom of the depression. The thinnest section at the thread is at least about eighty per cent of the thickness of the pipe wall at a point removed from the thread.

While I have shown and described a present preferred embodiment of my invention it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied within the scope of the following claims.

I claim:

1. Metal pipe having at one surface thereof a rolled thread whose side walls are substantially parallel to each other and having a substantially flat crest and throat, the opposite surface of the pipe having a helical depression whose dimension axially of the pipe at its bottom is not over about half the dimension of the crest of the thread axially of the pipe, the depression being disposed radially opposite the center of the thread crest, and a helical projection opposite the thread throat Whose dimension axially of the pipe is at least one-third greater than the dimension axially of the pipe of the thread throat and merging by a smooth curve into the depression, the pipe at such opposite surface being entirely free from sharp corners.

2. Metal pipe having at one surface thereof a rolled thread whose side walls are substantially parallel to each other, the opposite surface of the pipe having a helical depression Whose side Walls are inclined toward each other disposed radially opposite the center of the thread crest and a helical projection whose side walls are inclined toward each other opposite the thread throat, the depression and the projection merging into each other, the thinnest section at the thread being at least about eighty per cent of the thickness of the pipe wall at a point removed from the thread;

HARRY J. FINCH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 319,144 Stephens June 2, 1885 1,044,873 Felker Nov. 19, 1912 1,465,484 Richter Aug. 21, 1923 1,977,175 Davis Oct. 16, 1934 2,156,169 Unke Apr. 25, 1939 2,582,249 Hendel Jan. 15, 1952 

